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Eliminating Duplicate Values by using SELECT-DISTINCT statement

[Updated: Mar 30, 2018, Created: Mar 30, 2018]

The SELECT DISTINCT statement is used to return only unique results .

Example

The Entity

@Entity
public class Employee {
  @Id
  @GeneratedValue
  private long id;
  private String name;
  private String dept;
    .............
}

Using Query

public class ExampleMain {
  private static EntityManagerFactory entityManagerFactory =
          Persistence.createEntityManagerFactory("example-unit");

  public static void main(String[] args) {
      try {
          persistEmployees();
          findDistinctDept();
      } finally {
          entityManagerFactory.close();
      }
  }

  public static void persistEmployees() {
      Employee employee1 = Employee.create("Diana", "IT");
      Employee employee2 = Employee.create("Rose", "Admin");
      Employee employee3 = Employee.create("Denise", "IT");
      EntityManager em = entityManagerFactory.createEntityManager();
      em.getTransaction().begin();
      em.persist(employee1);
      em.persist(employee2);
      em.persist(employee3);
      em.getTransaction().commit();
      em.close();
  }

  private static void findDistinctDept() {
      EntityManager em = entityManagerFactory.createEntityManager();
      Query query = em.createQuery("SELECT DISTINCT e.dept FROM Employee e");
      List<String> resultList = query.getResultList();
      resultList.forEach(System.out::println);
      em.close();
  }
}
IT
Admin

Example Project

Dependencies and Technologies Used:

  • h2 1.4.197: H2 Database Engine.
  • hibernate-core 5.2.13.Final: The core O/RM functionality as provided by Hibernate.
    Implements javax.persistence:javax.persistence-api version 2.1
  • JDK 1.8
  • Maven 3.3.9

SELECT-DISTINCT Statement Example Select All Download
  • select-distinct-statement-example
    • src
      • main
        • java
          • com
            • logicbig
              • example
                • ExampleMain.java
          • resources
            • META-INF

    See Also